Push technology describes a style of Internet-based communication where a request for a given transaction is initiated by a publisher or central server. By contrast, pull technology is where the request for the transmission of information is initiated by a receiver or client. Push services are often based on information preferences expressed in advance, which is often called a publish/subscribe model. In such a model, a client subscribes to various information channels. Whenever new content is available on one of those channels, the server pushes information out to the user.
Synchronous conferencing and instant messaging are typical examples of push services. Chat messages and sometimes files are pushed to the user when they are received by the messaging service. Email is also a well-known push system. In typical Email configurations, an SMTP protocol is used as a push protocol. However, the last step—from mail server to desktop computer—typically uses a pull protocol like POP3 or IMAP. Modern e-mail clients make this step seem instantaneous by repeatedly polling the mail server, frequently checking it for new mail.
Icons are small graphic symbols (usually simple pictures) that denote programs, commands, data files, etc. in a graphical user interface. For example, an icon can be used to launch an application (e.g., open Microsoft® Word®). Dynamic icons are also known. For example, dynamic icons are icons that can be updated, changed or animated. However, an icon is small and the amount of information that can be displayed on the dynamic icon is limited.